<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>例选择器</title>
</head>
<body>
    <u1>
        <li>第一个节点</li>
        <li id="elem">第二个节点</li>
        <li class="el">第三个节点</li>
        <li class="el">第四个节点</li>
    </u1>
</body>
<script src="./js/jquery.js"></script>
<script>
    $("#elem").css("font-size", "72px")
    $(".el").css("background", "red")
    $("li").css("font-family","宋体")

    $("*").css("border","5px solid gold")
</script>
</html>